Tetranuclear Eu(III)-Co(II) complex of an N4O4 macrocycle

The reaction of an Eu(III) complex of the protonated form of the macrocyclic Schiff base derived from 1,3-diamino-2-hydroxypropane and 2,6-diformylphenol, [Eu(H₄L)Cl₃], with three equivalents of base results in a mononuclear complex of the triply deprotonated form of the ligand, [Eu(HL)]. The photophysical properties of the [Eu(HL)] complex are discussed on the basis of emission and excitation spectra, as well as of the emission decay times. The [Eu(HL)] complex in a reaction with cobalt(II) chloride gives a heterometallic Eu(III)-Co(II) macrocyclic complex, [EuCo(HL)(CH₃OH)₂Cl]₂Cl₂·4CH₃OH. In the presence of base and an excess of cobalt(II) chloride the starting [Eu(H₄L)Cl₃] complex is converted to a dinuclear Co(II) complex, [Co₂(H₂L)Cl₂(CH₃OH)₂]·1.5CH₃OH.     

Chelating effect in 4(5)-hydroxymethyl-5(4)-methylimidazole complexes

Light pink crystal of composition [Co(4-CH₂OH-5-CH₃im)₄](NO₃)₂ (where 4-CH₂OH-5-CH₃im denotes 4-hydroxymethyl-5-methylimidazole) were obtained from 2-propanol. The complex has been characterized by single-crystal X-ray as well as by electronic and vibrational spectroscopy. The immediate surrounding of the central ion is made up of four nitrogen atoms of the heterocyclic rings and two oxygen atoms of the hydroxymethyl group (CoN₄O₂ chromophore) The shape of the coordination polyhedron of the cobalt(II) ion is that of a slightly distorted octahedral.     

New dinuclear cobalt (ΙΙ, ΙΙΙ) and tetranuclear manganese (ΙΙΙ) complexes assembled by a polydentate Schiff-base ligand: synthesis,structure and magnetic properties

The reactions of 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propanediol (H₄L) and Mn(ClO₄)₂·6H₂O or Co(SCN)₂·3H₂O in the presence of triethylamine in methanol led to the formation of two new complexes [Mn^ΙΙΙ₄(HL)₂(H₂L)₂(CH₃OH)₄]·4CH₃OH·(ClO₄)₂ (1) and [Co^ΙΙCo^ΙΙΙ(H₂L)₂(CH₃OH)(SCN)]·1.5CH₃OH·1.5H₂O (2), respectively. According to structural data and magnetic properties tetranuclear complex 1 contains four homo-valence manganese (ΙΙΙ) atoms, while in the binuclear complex 2 composed of hetero-valence bi- and trivalent cobalt (ΙΙ, ΙΙΙ) atoms. Weak antiferromagnetic exchange interactions between neighboring manganese ions in 1 have place. χ_MT for 2 was fitted using a model of isolated cobalt (ΙΙ) ion with zero-field splitting parameters and the study confirms its mixed valence Co^ΙΙ/Co^ΙΙΙ nature. No slow magnetic relaxation effects were observed for both complexes in the absence of an applied dc magnetic field.     

Synthesis, Spectroscopic Studies, Crystal Structure and Electrochemical Properties of New Cobalt(III) Complex Derived from 2-Aminophenol and 4-(Dimethylamino)Cinnamaldehyde: Nano-Sized Complex Thin Film Formation via Surface Layer-by-Layer Chemical Deposition Method

New Schiff base (HL) ligand is prepared via condensation of 2-aminophenol and 4-(dimethylamino) cinnamaldehyde. The cobalt complex with the formula of [Co(L)₂(MePy)₂]PF₆ is prepared in good yield from the reaction of the ligand with cobalt(II) acetate. The compounds were characterized by the analytical and spectroscopic methods. The ligand (HL) behaves as a bidentate ligand and coordinates to the cobalt ions via the nitrogen and oxygen atoms with mononuclear structure. The ligand (HL) has been structurally characterized by X-ray crystallography. There is O–H···N–H bond linking the molecules together. FT-IR spectra show that HL is coordinated to the cobalt ion in a mono-negative bidentate manner with ON donor sites of the azomethene N and deprotonated phenolic-OH. There are two methylpyridine molecules apically coordinated to Co(III) ion in octahedral environment. Electrochemical properties were investigated as metal centres in the dimethylformamide solvents. The Co(III) complex exhibit both irreversible reductive (CoIII/CoII; Epc, −1.24 V) and oxidative (CoII/CoIII; Epa, +0.79 V, respectively) responses in cyclic voltammetry. Thin film of nano-sized [M(L)₂(MePy)₂]PF₆ complex was formed by surface layer-by-layer chemical deposition method. The formation of uniform thin films of nano-crystalline metal complex is dependent on metal and ligand concentrations.     

Di-μ-hydroxy macrocyclic ytterbium(III) complex

The mononuclear [YbracL]Cl₃·2H₂O and dinuclear [Yb₂(OH)₂Cl₂(racL)₂]Cl₂·4CH₃OH·2H₂O complexes of the macrocyclic ligand L derived from trans-1,2-diaminocyclohexane and 2,6-diformylpyridine have been obtained. The formation of the dinuclear species upon addition of hydroxide to the [YbracL]Cl₃·2H₂O or the enantiopure [YbrrrrL(NO₃)₂](NO₃) has been followed using ¹H NMR spectroscopy. The X-ray crystal structure of [Yb₂(OH)₂Cl₂(racL)₂]Cl₂·4CH₃OH·2H₂O complex has been determined. The complex is a dimer consisting of two macrocyclic units. The Yb(III) ion is coordinated by six nitrogen atoms of the macrocyclic ligand, two bridging OH groups and chloride anions. The chiral macrocycle L in this complex exhibits twist-bent conformation of approximate C₂ symmetry.     

The first example of half-sandwich cobalt(III) complex with hydrotris(pyrazolyl)borate ligand

This paper presents the synthesis, crystal structure and spectroscopic properties of a novel half-sandwich mononuclear cobalt(III) complex with hydrotris(3,5-dimethylpyrazolyl)borate ligand and thiocyanate [Tp^*Co(Hpz^*)(NCS)₂]·H₂O·CH₃OH (Tp^*: hydrotris(3,5-dimethyl- pyrazolyl)borate, Hpz^*: 3,5-dimethylpyrazole). The structure was determined by X-ray diffraction. The complex crystallizes in the monoclinic system, space group C_c, a=18.591(6) Å, b=10.536(3) Å, c=17.568(5) Å, β=11.284(5)°, Z=4, R₁=0.0501, wR₂=0.1179. The cobalt(III) ion in the complex is six-coordinated with nitrogen atoms, three from Tp^*, two from pyrazole and two from two thiocyanates, to form octahedral environment. The hydrogen atoms of O(2) of water molecule are connected by hydrogen bonds with S atoms of two adjacent complex molecules to form 1-D chains. The hydrogen atom of N(8) of complex molecule is connected by hydrogen bond with methanol. The spectroscopic results are consistent with the crystallographic study.     

Synthesis and Characterization of One-Dimensional Zinc(II) Coordination Polymers as Precursors for Preparation of ZnO Nanoparticles via Thermal Decomposition

Two new Zn(II) coordination polymers from the ligand, 2,5-bis(3-pyridyl)-3,4-diaza-2,4-hexadiene (bpdh), with different anions; i.e., [Zn(μ-bpdh)(H₂O)₄](ClO₄)₂·2bpdh (1) and [Zn(μ-bpdh)(H₂O)₄](NO₃)₂·2bpdh (2), were synthesized and characterized by IR spectroscopy, elemental analyses and X-ray crystallography. Compounds 1 and 2 are 1D coordination polymers and the zinc atoms are linked by four oxygen atoms from water molecules and two nitrogen atoms of bpdh ligands. There are two uncoordinated bpdh ligands that, along with the perchlorate or nitrate anions, form hydrogen bonds with water molecules. ZnO nanoparticles were obtained by thermolysis of 1–2 in oleic acid at 280 °C in air. The ZnO nanoparticles were characterized by X-ray diffraction and scanning electron microscopy.     

Synthesis, Crystal Structure, Spectroscopic and Thermal Properties of a Novel Complex of Hydantoin-5-acetic acid with Co(II)

The complex, tetraaqua bis(hydantoin-5-acetato) cobalt(II) was synthesized by the reaction of hydantoin-5-acetic acid and CoCl₂·6H₂O presence of NaHCO₃. The structure of the complex was determined by X-Ray single crystal data the thermal analyses, FT–IR and magnetic susceptibility data are also presented. The monoclinic crystal of the title compound, [Co(C₅H₅N₂O₄)₂(H₂O)₄], lie across centers of inversion in space group P21/c. The complex features a distorted octahedral [CoO₆] coordination with hydantoin-5-acetato and water ligands. The hydantoin-5-acetato anion is bonded to the cobalt(II) ion via its deprotonated carboxylic acid O atom. The complex molecules show three dimensional supramolecular networks by O–H···O and N–H···O interactions.     

Hydrothermal synthesis and tuning of size and morphology of α-Co(OH)2 and α-Co2(OH)3Cl nanostructures as precursors for nanosized Co3O4

This study aims to investigate the hydrothermally synthesized cobalt(II) hydroxide-based materials, which will be thermally converted to generate Co₃O₄ nanostructures; an important class of materials characterized by good electrochemical, catalytic and optical properties. First, cobalt(II) hydroxide nanostructures were prepared via hydrothermal hydrolysis of two different precursors (cobalt(II) chloride salt and dichlorobis(thiourea)cobalt(II) complex) exposure to an ammonia atmosphere, and then the obtained α-Co(OH)₂ and α-Co₂(OH)₃Cl nanostructures were calcined to produce Co₃O₄ nanostructures that were characterized by FT-IR, XRD, UV–vis DRS and SEM techniques. The effects of the nature of the precursor, its concentration, and of the temperature and reaction time on size and morphology of the product were also investigated.     

Doppler-Resolved Laser Probing of Photon-Initiated Bimolecular Collisions O(1D) + CH4 → OH(v,N) + CH3

The stereodynamics of the reaction O(¹D) + CH₄ → OH(v ≤ 4,N) + CH₃ at collision energies of ˜ 40 kJ mol⁻¹, has been probed via Doppler-resolved, polarized laser-induced fluorescence spectroscopy. Velocity-aligned, reagent O(¹D) atoms were generated under bulb conditions via polarized laser photodissociation of N₂O. Analysis of the Doppler profiles of nascent OH(v,N) fragments has allowed both scalar and vectorial product correlations to be determined, including differential scattering cross sections and rotational alignments. These imply the operation of a ‘delayed’ collision mechanism, dominated by the deeply attractive potential energy surface associated with the insertion to form CH₃OH; the intermediacy of a long-lived complex is excluded, however. Rotational angular momentum in the recoiling OH fragments is preferentially aligned perpendicular to, and azimuthally distributed about, their recoil velocity. The rotational excitation is thereby attributed to bending motion in the C···O···H plane during the reagent collisions. The scalar product pair correlations establish a near-zero translational exoergicity and anticorrelated internal energy distributions in the two reaction products.     

Synthesis and crystal structure of the mixed-valence trinuclear cobalt complex {[Co(CN)3(tBuNC)2](μ-CN)[Co(tBuNC)4](μ-CN)[Co(CN)3(tBuNC)2]}

The mixed-valence trinuclear cobalt compound {[Co(CN)₃(^tBuNC)₂](μ-CN)[Co(^tBuNC)₄](μ-CN)[Co(CN)₃(^tBuNC)₂]} is produced from the reaction of CoCl₂ with KCN and tert-butylisocyanide. In the resulting structure two cobalt atoms formally show the oxidation state +III, whereas the central cobalt still exhibits the formal oxidation state +II. All cobalt atoms are octahedrally coordinated by cyanide and isocyanide ligands. The supramolecular structure is determined by C–H⋯O and C–H⋯N hydrogen bonds linking acetone molecules to the trimeric complex as well as connecting the complex units into infinite chains.     

Six- and five-coordinated complexes of Co(II) with 2-(2′-pyridyl)quinoxaline. Crystal structures of the complexes [CoLCl2(DMF)] and [CoL2(H2O)2](ClO4)2·H2O·2CH3OH

Reaction of Co(II) perchlorate hexahydrate and anhydrous Co(II) chloride with the ligand 2-(2′-pyridyl)quinoxaline (L) leads to the formation of the novel five- and six-coordinated complexes CoLCl₂(DMF) (1) and [CoL₂(H₂O)₂](ClO₄)₂·H₂O·2CH₃OH (2), correspondingly. The crystal structures of the above complexes show a trigonal bipyramidal geometry around the metal atom for complex 1 and a distorted octahedral geometry for complex 2.     

The Effect of Cobalt on the Degradation of Methyl β-D-Gluco-Pyranoside by Oxygen in Aqueous Sodium Hydroxide Solution

Abstract

The effect of Co(II) (0 to 0.25 mW CoSO₄) on the degradation of methyl β-D-glucopyranoside (MBG) at 120°C in 1.25M NaOH with 0.68 MPa oxygen pressure was studied. When the Co(II) was increased from 0.00 to 0.01 to 0.05 mM the MBG half-life decreased from 12 to 6 to 1.5 hours, reflecting approximately a 0.5 order kinetic dependence on cobalt. An oxidation-reduction cycle between Co(II) and Co(III) involving oxidation of Co(II) by oxygen and oxidation of the glucoside by Co(III), hydroxyl radical, or superoxide is proposed for the degradation. At the 0.25 mM Co(II) addition level highly adsorptive Co(OH)₂ formed prior to reaction initiation with oxygen and removed otherwise soluble cobalt from solution. This resulted in lower rates of MBG degradation than obtained even at 0.01 mM Co(II) addition. However, Co(II) solubility could be enhanced if silicate anions or polyols (including MBG) were added to the alklaine medium prior to the Co(II) addition. In reactions initially containing 0.25 mM soluble Co(II), an adsorptive precipitate, presumably CoO(OH), gradually formed after reaction initiation with oxygen. Precipitation of the Co(III) solid coincided with a rapid decline in the rate of MBG degradation. Cobalt had little effect on the products of MBG degradation.     

Conversion of tetranuclear Ni complexes from a defect dicubane core to a [Ni4O4] cubane-like core via addition of 2-hydroxymethylpyridine: Synthesis,crystal structures,and magnetic properties

A defect dicubane-like complex, [Ni₄{(2-py)₂C(OH)O}₂{(2-py)₂C(OCH₃)O}₂ (N₃)₄]·2CH₃CN·2H₂O (1) and a cubane-like complex, [Ni₄{(2-py)₂C(OH)O}₃(hmp)₃(NO₃)]^.(NO₃)·3H₂O (2) (Hhmp = 2-hydroxymethylpyridine), were prepared by reacting NiCl₂·6H₂O with (py)₂CO, NaN₃ and NMe₄OH in MeOH/MeCN and the similar reaction exception the N₃⁻ anion replaced by multidentate chelating ligand Hhmp, respectively. X-ray analysis revealed that four Ni^2 + ions, four O atoms and two N atoms in 1 were located at the vertices of a defect dicubane; by contrast, four Ni^2 + ions and four O atoms in 2 occupied alternate vertices of a [Ni₄O₄] cubane. Magnetic studies indicated the presence of overall ferromagnetic interactions between Ni^2 + ions within both complexes.     

Oxygen storage/release in cobalt porphyrin electrodeposited films

In this work, ITO electrodes have been modified by means of the oxidative electrodeposition of two different cobalt porphyrins, CoTSPP and CoTMPyP, and the composition of such deposits have been studied by visible and reflection-FTIR spectroscopies. The data indicate that the porphyrin deposits are formed by a mixture of cobalt hydroxides, β-Co(OH)₂ and α-Co(OH)₂, and the porphyrin ring as radical. Moreover, the porphyrin electrodeposits absorb molecular oxygen as peroxo species (O₂²⁻), which has been detected in the films by IR spectroscopy, and which acts as a bridge between Co atoms (Co-O-O-Co). Also, monolayers containing a viologen derivative have been transferred onto the porphyrin-MIE (MIE, modified ITO electrode) by using the LB technique, and its redox process has been investigated. The results show an excellent mediator character of both cobalt electrodeposits throughout the viologen redox processes. Furthermore, the Co-porphyrin electrodeposits store atmospheric oxygen in a ratio proportional to the deposited porphyrin amount. This oxygen can be totally released from the porphyrin film via the electrocatalytic action of the viologen monolayer on top.     

Synthesis,structure and magnetic properties of a tetranuclear Mn(II) complex with carbohydrazone based ligand

A new tetranuclear complex of Mn(II), [Mn₄(L)₂(CH₃OH)₂(μ-N₃)₄(N₃)₂] ∙ 2(CH₃OH) (1), was synthesized and characterized by spectroscopic methods, single-crystal X-ray diffraction analysis and TGA analysis where HL is bis-[(E)-N′-(phenyl(pyridin-2-yl)methylene)]carbohydrazide. Single crystal X-ray analysis reveals that 1 has a Mn₄ core in which Mn(II) ions are connected by azide and enolate oxygen atoms. IR spectroscopy and X-ray analysis indicate that the carbohydrazone is coordinated to the metal cores as a mononegative ligand in the enol form. The magnetic behavior of 1 was investigated between 2 and 295 K and indicated that the magnetic coupling mediated via azide bridge is ferromagnetic whereas the enolate oxygen mediates antiferromagnetic coupling that leads to overall antiferromagnetic behavior.     

Producing superhard coatings by decomposition of complex salts in shaped-charge explosion

The behavior of two new complex salts containing cobalt and tungsten atoms was studied under different thermal conditions. It was found that when heated in air, the salt [Co(NH₃)₆](WO₄)NO₃ exploded at 260°C, and further heating to 800°C led to the formation of a mixture of oxide phases. Heating of [CoEn₃]₂(W₇O₂₄) · nH₂O was not accompanied by explosion and also led to the formation of cobalt and tungsten oxides. The complex salts were used to produce superhard (Vickers microhardness up to 35.8 GPa) coatings on titanium disks by means of shaped-charge explosion. High microhardness is associated with the formation of carbonitride crystalline phases on the target surfaces.     

Coordination versatility of 1,5-bis(salicylidene)carbohydrazide in Ni(II) complexes

Versatile coordination behavior of a polydentate Schiff base ligand 1,5-bis(salicylidene)carbohydrazide (H₃bsc) has been explored in Ni(II) complexes. [Ni(H₃bsc)₂](ClO₄)₂ (1)·H₂O·3CH₃CN is a bis chelate mononuclear complex of H₃bsc in keto form, and [Ni₄(H_0.5bsc)₂(O₂CCMe₃)₃(CH₃OH)₄](2)·2H₂O·2CH₃OH is a tetranuclear complex of H₃bsc with an unusual coordination. In 2, one phenolate group of the ligand coordinates in a monodentate way and the other coordinates in a μ₂-bridging mode to the Ni(II) center. This unusual coordination mode of the ligand stabilizes the Ni(II) complex in a tetranuclear form where the carbonyl oxygen of the ligand exists in between keto and enol form of bond order 1.5. Thus, complex 2, represents an unprecedented coordination behavior of the Schiff base ligand derived from carbohydrazides. Studies of magnetic properties of 2 are reported which reveal antiferromagnetic interaction between four Ni(II) centers.     

Synthesis, characterization and crystal structure of a novel co-ordination polymer [Co(BTB)2(NCS)2]n

A novel polymeric cobalt(II) complex with flexible ligand, [Co(BTB)₂(NCS)₂]_n 1 {BTB = 1,4-bis(1,2,4-triazol-1-yl)butane} has been prepared and structurally characterized by single-crystal X-ray diffraction as well as with elemental analysis, infrared spectroscopy and thermogravimetric analysis. The complex 1 consists of two discrete constituents, A and B, with the same chemical formula [Co(BTB)₂(NCS)₂] but different connecting mode. The six-co-ordination of Co²⁺ in A and B is in a distorted octahedral environment formed by four nitrogen atoms of the triazoles and two nitrogen atoms from two trans thiocyanato ligands. The structures of A and B demonstrate a one-dimensional neutral looped chain through two BTB-bridges and a two-dimensional network in which four BTB bridge four Co(II) atoms, respectively. A and B interpenetrate in an inclined fashion. The flexible BTB ligand exhibits three different configurations in 1.     

Syntheses and structures of a phenoxo-bridged copper(II) distorted cubane and related complexes with 2-hydroxy-N-(2-pyridylalkyl)benzamide ligands

Two new pyridylalkylamide ligands containing phenol groups appended to the amide, 2-hydroxy-N-(2-pyridylmethyl)benzamide (HL^PhOH) and 2-hydroxy-N-(2-pyridylethyl)benzamide (HL^PhOH′), were synthesized. Copper(II) complexes of these ligands were synthesized and characterized by X-ray crystallography, ESI-MS, FTIR, UV/Vis, and EPR spectroscopy. When basic Et₃N was used to deprotonate the ligands, tetracopper(II) [Cu₄(L^PhO)₄] (1) or dicopper(II) [Cu₂(L^PhO′)₂(CH₃OH)₂] (3) were formed. When base was not used, mononuclear [Cu(HL^PhOH)₂Cl₂] (2) resulted. Complex 1 possesses a distorted cubane-like structure, with the ligands bridging via the phenoxo oxygen atoms, and the copper atoms possessing a distorted square planar geometry. The ligands in dimeric complex 3 also bridge between copper(II) atoms via the phenoxo oxygen atoms, and the copper atoms are square pyramidal. Monomeric 2 is a tetragonally distorted six-coordinate species with pyridyl N atoms and chloride ligands in the equatorial plane, and long interactions with the amide carbonyl O atoms in the axial positions.